Upgrading two sites from 8.1 to 11.1 with new hardware

[jjdad]

Hello to all

I am in the process of upgrading two sites from 8.1 to 11.1.
The customer wants a complete forklift upgrade of everything, new chassis, modules, phones, etc. Not sure why they want to do this.
The new hardware will include a brand new chassis and modules, along with all new J179 phones.
I have put all the equipment together on the test bench and have loaded their old config, which upgraded and seems to work just fine for both systems.
Their VM is at the main location. The satellite office uses Centralized VM over an SCN.
My plan was to upgrade the satellite office first, then upgrade the main site a day or so later.

My question is this….

If the main site is running 8.1 software, will the satellite office running 11.1 still talk to the main site running 8,1 and will the VM still work?
Or should I upgrade the main site first as it has the VM module?
Due to their operation schedule and the number of extensions, I cannot do both at the same time.
Has anyone done this before and what were your results?

Thanks!

 

[ipohead]

I recall SCN will work from 11.0 to 8.1 for dialling extensions but not for centralized voicemail.

Could they cope with embedded voicemail for a day?